1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) and, more particularly, to a semi-transmissive VA LCD capable of securing a wide viewing angle and also securing a light transmittance of a transmissive region and that of a reflective region.
2. Discussion of the Related Art
Generally, liquid crystal displays (LCD) are quite useful because of their characteristics such as light weight, slim design and driven at a low power consumption. Thus, LCDs are commonly used as mobile electronic devices such as notebook computers, mobile phones.
The LCD displays a desired image on its screen by controlling the amount of transmission of light according to a video signal applied to a plurality of controlling switching elements arranged in a matrix form.
The LCD includes a liquid crystal panel including a color filter substrate, an upper substrate, and a thin film transistor (TFT) substrate, a lower substrate, and a liquid crystal layer filled therebetween, and a liquid crystal panel driver that supplies a scan signal and image information to the liquid crystal panel to operate the liquid crystal panel.
Compared with a CRT (Cathode Ray Tube) or an LED (Light Emitting Diode), the LCD is not a self-emissive display device that does not emit light by itself, so it requires a backlight assembly for providing light to the liquid crystal panel.
The LCD can be divided into two types according to types of light sources: a transmissive LCD using a light source provided therein; and a reflective LCD using an external light source (e.g., solar light).
The transmissive LCD uses an internal light source using a mobile battery or the like as a power source, which consumes much power. Thus, when the transmissive LCD is applied to a mobile electronic device, a usage time is not long due to the capacity of the mobile battery, which can cause a problem in that the advantage of portability cannot be fully exerted.
In the case of the reflective LCD that uses an external light source such as solar light, when the reflective LCD is in use in a room, the intensity of the external light source is not strong, making the screen rather dark, which results in degradation of quality of screen images.
Thus, in an effort to solve these problems, a transflective LCD including characteristics of both the transmissive LCD and the reflective LCD has been proposed. With its advantage of low power consumption, the transflective LCD is easily applicable to a mobile electronic device and displays a quality screen image even in a room as well as in an outdoor space.
The transflective LCD will now be described with reference to the accompanying drawings.
The general LCD as shown in FIG. 1 is a transflective VA (Vertical Alignment) LCD including a first substrate 1 and a second substrate 2 having a transmissive region and a reflective region.
Although not shown, gate lines and data lines are formed to cross vertically and horizontally to define a plurality of pixels on the first substrate 1, and a thin film transistor (TFT) is formed at each crossing of the gate lines and data lines of each pixel. Here, a gate electrode 9 of the TFT is connected with the gate line, a source electrode 12 is connected with the data line, and a drain electrode 13 is connected with a pixel electrode 7. A reflective layer 3 having a plurality of embossed portions and a vertical alignment layer 8 are formed at a reflective region of the first substrate 1.
A color filter layer 16 for displaying color is formed on the second substrate 2. A common electrode 5 is formed on the color filter layer 16 to form a vertical electric field together with the pixel electrode 7 formed on the first substrate 1 to apply electric field to a liquid crystal layer 4. A vertical alignment layer 6 is formed on the common electrode 5.
Rib structures 19 protrude in the direction of the first substrate 1 and are formed on the second substrate 2. The rib structures 19 serve to divide the electric field formed by the pixel electrode 7 and the common electrode 5 into multi-domains, according to which the liquid crystal layer 4 forms the multi-domains as shown in FIG. 1.
However, while the rib structures 19 allow the electric field formed by the pixel electrode 7 and the common electrode 5 to form multi-domain to allow a user of the LCD to view a screen image of a wide viewing angle. The ambient region of the rib structures 19 has a relatively low light transmission efficiency, degrading a light transmittance of the transmissive region and a light reflectance (reflectivity) of the reflective region. This results in partial deterioration of the luminance of a screen image of the transflective VA LCD to degrade picture quality.